The first commit reverts the revert of #23787.
The second fixes lambdalifting in convolutedly nested
closures/closureiters. This is considered to be the reason of #24094,
though I can't tell for sure, as I was not able to reproduce #24094 for
complicated but irrelevant reasons. Therefore I ask @jmgomez, @metagn or
anyone who could reproduce it to try it again with this PR.
I would suggest this PR to not be squashed if possible, as the history
is already messy enough.
Some theory behind the lambdalifting fix:
- A closureiter that captures anything outside its body will always have
`:up` in its env. This property is now used as a trigger to lift any
proc that captures such a closureiter.
- Instantiating a closureiter involves filling out its `:up`, which was
previously done incorrectly. The fixed algorithm is to use "current" env
if it is the owner of the iter declaration, or traverse through `:up`s
of env param until the common ancestor is found.
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Co-authored-by: Andreas Rumpf <rumpf_a@web.de>
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